What Is the Aortic Hiatus?

The aortic hiatus is an opening in the diaphragm of the body through which the aorta passes. It is lowest- and rearmost-positioned of the diaphragm's large apertures, and it is formed by the sheet's curved ligaments. The aortic hiatus is also known as the aortic aperture.

Also known as the thoracic diaphragm or midriff, the diaphragm separates the thoracic and abdominal cavities. The approximate location of the aortic hiatus in the diaphragm is around the level of the T12, which is an abbreviation for the 12th thoracic vertebra. This opening can also be described as being slightly to the left side of the diaphragm's middle line.

The aorta is not the only structure that passes through the aortic hiatus. Also traveling through it is the thoracic duct, which is the largest vessel of the lymphatic system. Passing through the right of the aperture, it plays a part in circulation by draining lymph into the blood via the left subclavian vein.

A third structure that runs through the aortic hiatus is the azygous vein. Like the thoracic duct, it functions as part of the circulatory system by providing a path of blood to the heart's right atrium when there is a blockage of the vena cava vein. Occasionally though, the azygous vein travels up the thoracic vertebral column's right side instead.

Anteriorly, the aorta hiatus is next to the esophagus. This means that the muscular tube, which is part of the digestive system, is in front of the opening. Posteriorly, or at the back, is the T12 and the azygous vein. To the right is the inferior vena cava.

In the strictest sense, the aortic hiatus is not an opening in the diaphragm. Rather, it is situated between the diaphragm and the vertebral column. Such a location means that the hiatus is actually behind the diaphragm. Thus, any contractions that the sheet makes does not directly impact the aorta. It is also posterior to other apertures, such as the esophageal hiatus, which is located around the level of T10 and is named so since it provides a passage for the esophagus.

The aortic hiatus was once widely described as an osseoaponeurotic opening. This means that it is placed in an area formed by bone and tendinous layers. Indeed, the adjective is formed with the combination of the Latin word osseus, which means "bone," and the Greek words apo and neuron, which describe an area where muscles become tendons. The compound word, however, is no longer commonly used.